The present invention relates to a carburetor for an internal combustion engine having a piston valve in an intake channel which cooperates with a fuel discharge nozzle to regulate the mixture of air and fuel at a mixture region in the intake channel and, more particularly, to such a carburetor in which drive means position the piston valve in the intake channel in response to distinct control means the operation of which is dependent upon the operating conditions of the internal combustion engine.
Carburetors for internal combustion engines mix fuel with air to provide a desired mixture of air and fuel for operating the engine. One type of carburetor has a throttle valve in an intake channel for regulating the volume of the air-fuel mixture provided to the engine to control the operation of the engine. A fuel discharge nozzle is positioned on the intake channel, upstream of the throttle valve, and opposite a piston valve. The piston valve movably extends into the intake channel to vary the cross section of the channel. A conical needle valve extends from the piston valve into a fuel exit aperture of the nozzle to also vary the cross section of the aperture through which fuel can flow into the intake channel in response to the position of the piston valve in the intake channel.
When the throttle valve opens or closes to change the volume of the air-fuel mixture flowing to the engine, the piston valve moves out of or into the intake channel to control the speed with which the corresponding volume of air flows past the piston valve and fuel discharge nozzle. The air passing the exit aperture of the nozzle creates a negative pressure or aspirator-like suction at the aperture which draws fuel through the aperture into the intake channel for mixing with the air in a mixture region of the intake channel between the piston valve and nozzle and the throttle valve. The suction is a function of the speed of the air passing the fuel exit aperture of the nozzle and greater suctions draw the fuel through the aperture at greater rates. The rate of fuel flow through the aperture and the cross section of the aperture through which the fuel flows determine the volume of fuel drawn into the intake channel. The ratio of the air volume entering the mixture region past the piston valve and the fuel volume drawn from the nozzle by the passing of this air determines the richness of the air-fuel mixture.
The desired richness of the air-fuel mixture is determined by the operation of the internal combustion engine. The air-fuel richness is substantially constant for an engine; however, the richness is often desirably increased for more open positions of the throttle valve which correspond to higher speed or greater power operation of the engine. Moreover, it is often desirable to increase the richness of the air-fuel mixture during periods of engine acceleration or increasing power which correspond to opening movement of the throttle valve.
Therefore, a carburetor of the type described operates by moving the piston valve in the intake channel to vary its cross section and provide a substantially constant speed to the volume of air passing the nozzle and a corresponding change in the cross section of a fuel exit aperture through which fuel flows from the nozzle into the intake channel by moving the needle valve in the fuel exit aperture with the movemement of the piston valve to maintain the desired richness of the air-fuel mixture. To provide a richer mixture for more open positions of the throttle valve, the cross section of the intake channel is limited by the piston valve to increase the speed of the air flowing past the piston vlave and the nozzle which thereby increases the suction at the exit aperture of the nozzle to draw a higher volume of fuel from the aperture relative to the volume of the air passing the aperture. Similarly, when it is desired to increase the richness of the mixture during opening movement of the throttle valve for acceleration of the engine, the speed with which the piston valve moves to increase the cross section of the intake channel is damped relative to the speed with which the throttle valve is opening to transiently increase the speed of the air passing the piston valve and nozzle and thereby transiently increase the richness of the air-fuel mixture.
Known devices for moving the piston valve in the intake channel in response to the operating conditions of the internal combustion engine determined by the position of the throttle valve in the intake channel are mechanically combined with means detecting the operating conditions of the engine in response to which the piston valve is to be moved. These combined piston valve moving means and engine condition responsive means operate from pressure differentials in the intake channel upstream and downstream of the piston valve which are produced by the relative positions of the piston valve and throttle valve. Such mechanical devices have sufficiently high operating friction relative to these small, pneumatic actuating forces to interfere with proper movement of the piston valve. The operating friction may additionally introduce hysteresis into the operation of the piston valve to further impede its proper operation. Moreover, such known carburetors can only be operated with the piston valve in an essentially vertical position with the air intake channel into which the piston valve extends then being essentially horizontal. Such transverse draft carburetors may not be desired.